A key Democratic U.S. senator, Ben Cardin of Maryland, has come out against the international agreement with Iran to curb its nuclear program.

Cardin is the ranking member on the Senate Foreign Relations Committee and considered to be one of the most influential senators and thus could have an impact on how others decide to vote.

In an opinion piece for The Washington Post, Cardin said that after lengthy consideration, he had concluded that the Joint Comprehensive Plan of Action negotiated with Iran legitimizes Iran's nuclear program. Cardin also wrote that after 10 to 15 years, it would leave Iran with the option to produce enough enriched fuel for a nuclear weapon in a short time. He said a vote of this nature should be a vote of conscience, and not a vote of party loyalty.

Cardin's decision is seen as a setback to a push by the Obama administration to win the 41 Democratic votes needed to be able to block a vote of disapproval by the Senate.

But the president also got some good news Friday, with Democratic Senator Michael Bennet of Colorado coming out in support of the deal. A total of 38 Democratic senators now support the deal and only three oppose it.

The deal has virtually no Republican support in either the House of Representatives or the Senate.

Both chambers are set to vote to approve of or reject the Iran nuclear deal by September 17. House Majority Leader Kevin McCarthy, a California Republican, has said the House plans to vote on a measure of disapproval by September 11. A vote of disapproval is almost certain to pass in the House, with its large Republican majority.

If a measure of disapproval is passed in either chamber, President Barack Obama would veto it, and it appears that he has the Democratic votes needed to sustain a veto in both the House and the Senate.

Republican critics of the deal say it will make the world less safe by giving Iranian leaders a cash bonanza and boosting their international standing.

Republican Senator Ted Cruz of Texas, who is running for president, invited his fellow Republican candidate, businessman Donald Trump, to appear with him at the U.S. Capitol next Wednesday at a rally to oppose the Iran nuclear deal.